TDL Studio 1 loudspeaker

TDL is part of ELAC, one of the most successful OEM drive-unit manufacturers in the UK, particularly renowned for the 1" aluminum-dome tweeter that they make for Monitor Audio, Acoustic Energy, and British Fidelity (footnote 1). Perhaps of even more interest to readers of Stereophile is that the TDL system designer is one John Wright, who designed the classic series of IMF loudspeakers (footnote 2) and who also was one of the leading equipment reviewers in the UK back in the 1960s. (For a while John was also a contributor to this magazine, his comprehensive reviews of tonearms appearing in Vol.2 Nos.10 & 12.)

The IMF designs represented the first commercially successful application of the "transmission-line" woofer-loading principle, and the TDL models continue that tradition. Even though the Studio 1 ($1445/pair, not including stands) is the smallest speaker in the TDL range, it still loads its 6.5", Cobex-coned woofer with a resistively damped line that is intended to absorb the cone's back wave. (The cabinet interior contains internal partitions that produce a folded line.) In practice, the short line possible in the modest-sized enclosure cannot totally absorb the sound, so it is arranged to vent at the foot of the front baffle, its output supplementing the frontal radiation of the woofer in the bass to give good low-bass extension. A practical transmission line therefore takes on some of the characteristics of a reflex design.

A two-way design, TDL's Studio 1 uses a version of the same aluminum-dome tweeter that appears in the Acoustic Energy AE2. This is mounted vertically beneath the woofer, an arrangement that, provided the correct drive-unit electrical polarities are observed, tilts the main response lobe upward toward the listener's earimportant in a modest-sized speaker such as this. The crossover circuitry is mounted on a printed circuit board fastened to the rear of the terminal panel, which has four knurled, gold-plated, all-metal binding posts to allow the speaker to be biwired. The crossover is relatively simple, a series non-polarized electrolytic capacitor in the tweeter feed providing a first-pass high-pass slope, with a series resistor to lower the tweeter level; the woofer filter is basically second-order low-pass, with a series air-cored coil and a shunt electrolytic capacitor. There is also an RC Zobel network shunting the drive-unit terminals.

The Studio 1 cabinet has a small plinth attached to its base which slots into a small space-frame stand, some 4" high, which is fitted with carpet-piercing spikes. A pair of these stands costs $180, but as the Studio 1 really does need the stand to sound its best, in my opinion, it's a shame that they are not included in the purchase price. Surprisingly at this price level, though the cabinet sides, top, and bottom are finished in real wood veneer, neither of the drive-units is rebated into the black-painted baffle. The woofer frame does have a degree of profiling, however. The grille consists of brown jersey cloth stretched over a fiberboard frame. Though its internal edges do have a slight flare in the vicinity of the drive-units, it appears to present a significant acoustic obstruction, so I left it off for most of the auditioning (see later).

The Sound
Preliminary listening suggested that it was important not to sit at too high a listening position with the Studio 1s, an audible "hollowness"probably due to a crossover suckoutdeveloping when you can see a significant amount of cabinet top. I therefore used the adjustable spikes to ensure that my ears were in line with the cabinet top, which gave the smoothest response trend at my listening seat with pink noise. (I sat 8' from the speakers; because the tweeter-under-woofer topology results in a slightly tilted-up main response lobe, the further you sit from the Studio 1s, the less critical will be this transition between flat and hollow-sounding treble.) Slight but persistent excesses of energy in two regions could still be heard on the optimum axis with pink noise, however, one in the midrange centered around 750Hz or so, the other in the mid-treble. It remained to be seen how audible these would be with music. (Noise signals are usefulread, notoriousfor revealing slight balance problems.)

I couldn't resist the temptation: having been exposed to years of being told how good the bass is of a transmission-line speaker, I broke my rulesI normally start my auditioning with spoken voiceand reached first for an organ recording, the Telarc Bach set from Michael Murray (CD-80088), which features the infamous Toccata and Fugue in d. (Trivia lovers might be interested to learn that this most organic of all organ works was probably originally written for violin!) I was not disappointed. Though the very lowest notes did lack substance, the reproduction of the pedals was excellent for what is basically quite a small two-way speaker with a single 6.5" woofer. The only indication that this was a smallish two-way was at high replay levels, when things became rather congested. In fact, this congestion set an upper replay-level limit of around 95dB in my room, which may not be enough for some tastes. In this respect, the Studio 1 fell considerably behind the Acoustic Energy AE2.

Upon further listening, however, it became apparent that not all the congestion could be laid at the feet of the woofer's limited radiating area. At the end of the Fugue in D on the Telarc disc, the organ pedals take up the half-scale passage that has been the subject of the fugue. Even at moderate replay levels, there was some confusion in the upper bass that somewhat obscured pitch definition.

Rob Wasserman's double bass, on the "Ballad of the Runaway Horse" from his Duets album (MCA MCAD 42131), was also rather lumpy in this same region, and when he duets with himself on this album, in the Aaron Neville track "Stardust," for example, the two double basses tended to interfere with one another's sounds to a greater extent than through either of the other two loudspeakers reviewed this month. Spoken male voice also had a rather chesty quality, there being an underlying bass "grumble" to the voice character, similar to that obtained when you speak too close to a directional microphone, and low-pitched drums sounded rather "slow." However, this wasn't to anything like the same degree as with a typical high-Q reflex design, and in fact it was the excellent clarity and extension of the mid- and lower bass that accentuated its audibility.

Moving higher up in frequency, the midrange was clean, apart from a slight "hoot" noticeable on piano and female voice around the top of the treble staff (the 600$n800Hz region), where it made the latter sound rather "shouty." This was less noticeable on orchestral music than it had been on voice, piano, and pink noise, however, and the upper midrange and treble were very smooth, overall. There was a slight wispiness to the extreme highs, however, that slightly accentuated the wire-sound of a typical snare-drum, and was unkind to the sound of closely miked violins. Naturally miked violins were presented with just the correct degree of astringence. (This was via the dark-toned Kinergetics KCD-40 player; via the brighter Proceed, there was too much treble energy.)

Where the Studio 1s scored, however, was the way they presented a good sense of recorded space. The guitar and double-bass track on the StereophileTest CD is a good test of this: the way in which the guitar's upper register slaps the surrounding chapel acoustic into motion seems to be very system-dependent. Via some speakers, although the instruments' tonalities are reproduced correctly, the "space" on the recording, that I heard from the microphone feeds, is almost entirely diminished. Via the TDLs, however, you could well hear the dome of ambience around and behind the instruments. Midrange images seemed to be a little more forward than strictly accurate, to judge by the way the speakers reproduced my own piano recordings, but there was still a considerable degree of depth apparent. The horns, for example, at the start of the Ashkenazy/Philharmonia recording of Sibelius's Karelia Suite (London 414 534-2), were set way back. And on Stereophile's Poem LP, though the tonal balance was a little on the "cold" side, the piano was set the correct distance behind the stable flute image. It was actually listening to this track with the grilles on that convinced me that they were a sonic no-no. The grilles rendered the piano both less well-defined in space, and too forward.

Conclusion
When auditioning the TDL Studio 1s, be sure that the grilles are removed and that you are on the optimum listening axis, as the balance is otherwise unmusically hollow-sounding, with the upper treble left unsupported. The short stands are essential to achieving this, in my opinion. But on the correct axis, and provided the replay level isn't too high, the Studio 1 will provide a good degree of low-frequency extension for such a small speaker. The colorations noticed in the upper bass and midrange were a little too apparent for my tastes, but as the audibility of both will be very much dependent on music type, they may or may not detract from the clean, detailed treble and excellent imaging offered by these speakers.

At $1625/pair including stands, the Studio 1 comes under strong competition from the Magnepan MG2.5R and Vandersteen 2Ci, both of which will play louder without strain or congestion, but it is sufficiently differently balanced from either that it could well find a successful niche in the US market.

Footnote 1: After ELAC was purchased by Harman in 1989, John Wright organized a management buyout of the TDL brand.

Footnote 2: "IMF" stood for Irving M. ("Bud") Fried, who was associated with John for a long while. When John and Bud split up, however, the English company retained the rights to use the name IMF, which is why Bud's own brand of American loudspeakers, some of which also feature transmission-line bass and midrange loading, are known as "Fried."

Thanks John, that answer stirs up a distant memory of the two. It probably explains why I happened to use an ELAC drive unit in the first loudspeaker that I built aged 15 at school in London back in the 60s. Considering that the idea of tweeters and crossovers was beyond me , using imported drivers would have been inconceivable.

Not really. The IMF TLS 80 impressed the heck out of me when I first heard it in the 1970s - the combination of the Celestion HF1300 soft-dome tweeter and Coles 4001 supertweeter produced some of the best high frequencies I had experienced at that time. John Wright struck me back then as a very talented designer who continued that pedigree with TDL.

hollowman wrote:

If so, what was your first negative experience with TDL?

It wasn't so much a negative experience with TDL but the fact that over the years I became dissatisfied with so-called "transmission-line" speakers that didn't load the woofer with a true line. Such designs almost always had a line resonance in the upper bass that colored the sound too much for my taste. This small TDL had such a problem, as revealed by the impedance trace and my auditioning comments.

Indeed. There were a number of smaller TLs but the concept doesn't scale down very well. The volume of the chamber behind the LF driver and the entry port from that chamber into the upper part of the line are critical for decoupling the line from the driver. Those dimensions are frequency-dependent while the smaller TLs, unfortunately, scaled them down in relation to the driver size. The opening at the other end of the line, conversely, was uncritical

John Wright was gracious to send me his notes on the TLS80 design penciled in on a copy of his HFN article. I built a larger version of it and the KEF B139 performance was remarkably flat (although I admit to using a lower crossover than in the original).